The FLIR camera shows both heat and CO₂. In order to see CO₂, we have to blind the FLIR camera to all that it can see, except for a very small portion of the electromagnetic spectrum. Think of it as a glass that only lets one shade of green through. This is known as a band pass filter. Since we know that CO₂ has a “shade of color” in the 4 micron range, we can use a band pass filter in that range, and this will result in images that appear brighter and darker in otherwise homogeneous areas when CO₂ is present in various concentrations. We still see heat, but the heat we see is dimmed and brightened by the presence of the CO₂. This is known as signal attenuation.